Phytochromes and Cryptochromes in the Entrainment of the <i>Arabidopsis</i> Circadian Clock

TLDR

Circadian clocks are entrained by light, with phytochrome B mediating high‑intensity red light, phytochrome A and cryptochrome 1 handling low‑intensity red and blue light, and the conservation of cryptochromes across plants and animals indicating evolutionarily conserved input pathways. Photoreceptor‑deficient Arabidopsis thaliana mutants were used to assess how light fluence rate affects circadian period.

Abstract

Circadian clocks are synchronized by environmental cues such as light. Photoreceptor-deficient Arabidopsis thaliana mutants were used to measure the effect of light fluence rate on circadian period in plants. Phytochrome B is the primary high-intensity red light photoreceptor for circadian control, and phytochrome A acts under low-intensity red light. Cryptochrome 1 and phytochrome A both act to transmit low-fluence blue light to the clock. Cryptochrome 1 mediates high-intensity blue light signals for period length control. The presence of cryptochromes in both plants and animals suggests that circadian input pathways have been conserved throughout evolution.